Exposure to mold is also likely to be correlated with socioeconomic status, especially in more humid parts of the country. Think what kind of people are most likely to live in rundown houses (or even basements!) barely above the water table, without a functioning HVAC unit.

Mold is the kind of problem that is at most a nuisance for people who have the means to do something about it, but seemingly unsolvable for people who actually need a solution.